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Ecology (BIOL 250)
Lecture 15:
Patterns of Life Histories
AnnouncementsToday’s Outline
Offspring Numb er Versus
Size
Animals
Plants
Life History Vari ation Among
Species
Life History Clas sification
R - Selected
K - Selected
New Models
Sexual selection
Offspring Number Versus Size
!Principle of Allocation: If organisms use
energy for one function such as growth,
the amount of energy available for
other functions is reduced.
"Leads to trade-offs between functions such
as number and size of offspring.
!Semelparity
"Initially, invest all energy in growth and storage.
"Followed by one massive suicidal act of
reproduction (examples?)
! Iteroparity
"Produce fewer offspring at a time.
"Repeat reproduction throughout their lifetime.
(examples?)
Offspring Number Versus Size
Seed Size and Number in Plants
!Many families produce small number of
larger seeds. . . But some produce a
great number of tiny seeds.
"Dispersal mode influences seed size.
!What are some examples of dispersal modes?
!Why might they influence seed size
Seed Size and Number in Plants
!Westoby et.al. recognized six seed
dispersal strategies:
"Unassisted: No specialized structures.
"Adhesion: Hooks, spines, or barbs.
"Wind: Wings, hair, (resistance structures).
"Ant: Oil surface coating (elaisome).
"Vertebrate: Fleshy coating (aril).
"Scatterhoarded: Gathered,stored in caches.
Seed Size and Number in Plants
!Jakobsson and Eriksson (2000) found
seed size variation explained many
differences in recruitment success.
"Larger seeds produce larger seedlings and
were associated with increased recruitment
(seed production).
